Rotary air compressors



July 31, 1962 c. H. BRISCOE 3,047,212

ROTARY AIR COMPRESSORS Filed March 24, 1958 INVENTOR GEORG-E H. Bm'scogUnited tates Patent 3,047,212 ROTARY AIR COMPRESSORS George HaroldBriscoe, Beddington, Croydon, England,

ass'ignor to Lacy-Hulbert & Company Limited, Beddington, England FiledMar. 24,1958, Ser. No. 723,158 Claims priority, application GreatBritain Apr. 2, 1957 2 Claims. (Cl. 230-210) This invention concernsimprovements in air (or gas) compressors and exhausters (hereinafterreferred to as compressors) and is especially concerned with the socalled dry-type of rotary compressor which employs vanes of specialcomposition working in slots in a drum mounted eccentrically within thecompressor casing, though it is also applicable to positive displacementrotary blowers or piston or diaphragm operated compressors.

Air compressors must be effectively cooled if their efficiency is to bemaintained and this is particularly true of the dry rotary type. In thistype of compressor or exhauster, for example, the vanes are made ofmaterial which is liable to lose its strength and form if it issubjected to a temperature above a critical range: the bearings alsorequire efiicient cooling. 7

It has been found possible to cool the smaller sizes of dry rotarymachines by fitting a fan to the rotor shaft which directs air over thecompressor stator housing. On larger sizes of machines however it isfound that the restriction in speed of revolution of the rotornecessitated by consideration of blade rubbing speed is such that no fanof reasonable dimensions fixed to the rotor shaft is capable of passingan appropriate amount of air and overheating necessarily takes place.

. It is the object of the present invention to provide an eilectivelycooled air compressor without having recourse to liquid circulation orother expensive and complicated cooling systems.

According to the invention, from one aspect, we provide an aircompressor whose rotor shaft or piston crankshaft derives its drive froma motor or prime mover which is arranged to drive a fan (whose outlet isdirected over the surface of the compressor) at higher speed than thatat which the rotor or piston crankshaft is driven.

The speed increase of the fan drive may be attained by the use ofdifferential pulley sizes or by gearing.

From another aspect the invention provides a rotary vane air compressorhaving a driving pulley fixed to its rotor shaft and a further pulleymounted for free rotation and carrying a fan whose output is directedover the compressor, said further pulley being arranged to be driven athigher speed than the rotor shaft by the same motor or prime mover thatdrives that shaft.

The fan pulley is conveniently carried loosely upon the compressor rotorshaft.

In preferred forms of the invention the pulley carrying the fan isarranged to be driven in the same direction of rotation as is the rotorshaft, so that the speed of rotation of its bearing relative to therotor shaft is reduced.

The fan employed is preferably of the radial-flow type as used forcooling electric motors, and a guide plate with a central air inlet eyeis preferably fitted to direct the air flow from the fan over thecompressor stator body, which may be formed with cooling fins.

The above and other parts of the invention are embodied in one preferredform of compressor or exhauster which will now be described in greaterdetail by way of example with reference to the accompanying drawing;which. is a central vertical section.

The compressor comprises a stator casing 1, which is deeply finned as at2 on its outer surface 2 for cooling ECQ purposes and which is closed atboth ends by cover plates 3 and 4 which incorporate bearing housings.

The drum 5 of the compressor is of a type known per se provided with anumber of slots in which slide vanes 6 of a special composition as thedrum turns eccentrically within the stator housing.

The driving shaft 7 of the drum extends through'the end plate 3 and isprovided with a key-way 8 by which is fitted a first pulley 9 for driveby belts 16 and 17 from the pulley 18 of an electric motor 19.

The driving shaft 7, between the driving pulley 9 and the drum 5,carriesthe inner race of a ball-bearing 10 upon which is mounted asecond driving pulley 11 of smaller diameter than that which drives theshaft. This second pulley 11 is free to rotate relative to the drumdriving shaft and has bolted to it by bolts 12 a multibladed radial-flowfan 13.-

An air guide plate or cowl 14 having a central opening opposite the eyeof the fan 13 is carried by brackets (not shown) from the stator 1 in aposition to guide the air delivered from the fan outlet 15 axially ofthat stator.

The pulley 18 on the motor shaft is connected by a belt 20 to the fandriving pulley 11 and this motor pulley may be of the same size as thatdriving the drum 5 or larger if necessary in order to impart to the fan13 a rotational speed considerably higher than that of the drum shaft 7.

In experiments carried out with proto-type machines of relatively largesize it has been found, that, whereas a fan driven at drum speed isquite incapable of cooling the compressor stator effectively, the highspeed fan of the invention is easily capable of maintaining an air flowsuch that operating temperature conditions are kept within safe limits.

It will be understood that the invention is not restricted to thedetails of the specific embodiment described which may be varied withoutdeparting from the scope of the following claims.

I claim:

1. The combination of an air compressor of the rotary vane type having acasing, fins on the outer surface of said casing, compression meanswithin the casing, a continuous, integral rotary shaft extendin g withinand outside of said casing for driving said compression means, a firstdrive means keyed to said shaft outside said casing, a second drivemeansfreely mounted upon said shaft outside of said casing, a fan rotatablymounted on said shaft and directly connected to said second drive meansto be driven thereby, said fan having blades arranged to blow coolingair over the finned outer surface of said compressor casing, said seconddrive means being arranged on the shaft between the casing and saidfirst drive means and constructed to drive said fan at a higher speedthan said first drive means drives said compression means.

2. The combination of an air compressor of the rotary van-e type havinga casing, fins on the outer surface of said casing, vane compressionmeans within the casing, a continuous, integral rotary shaft extendingwithin and outside of said casing for driving the vane compressionmeans, a first drive pulley keyed to said shaft outside said casing, asecond pulley freely mounted upon said shaft outside said casing, and afan rotatably mounted on said shaft and directly connected to saidsecond pulley means the fan will be driven at higher speed than thecompressor.

References Cited in the file of this patent UNITED STATES PATENTS HighamJuly 9, 1946 Jones Apr. 18, 1950 Willcox Nov. 29, 1955 Hockel Mar. 10,1959 Scheiterlein Dec. 15, 1959 FOREIGN PATENTS Germany May 19, 1930Great Britain Apr. 16, 1948

